1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to a ZnO film formed with a C-axis orientation, as a result of an underlying amorphous Al2O3 layer.
2. Description of the Related Art
As-deposited thin film ZnO, deposited using an atomic layer deposition (ALD) process, has a low C-axis orientation and a small crystal size. It is well known that crystal-matched substrates can be employed to guide the crystallization of an overlying thin film. For example, C-axis ZnO films can be formed using epitaxy and epitaxial lateral overgrowth processes. These methods are slow, require high temperatures, and require a crystalline substrate or seed layer. It has also been reported that well-aligned vertical ZnO nanowires can be grown on crystal-matched substrates, such as sapphire or GaN. It has been reported that high C-axis, and even epitaxial, ZnO films can be grown on sapphire substrates, where a sapphire substrate is single-crystal Al2O3.
Nanostructured materials such as nanowires, nanorods, and nanoparticles, have potential for use in applications such as nanowire chemical and bio sensors, nanowire LEDs, nanowire transistors, nanowire lasers, to name a few examples. Materials such as ZnO have been made into nanostructures, when the growth is properly controlled. ZnO is a photo-luminescent (PL) material of interest that exhibits an intrinsic UV PL at 380 nanometers (nm) and a defect-related visible PL broadly centered around about 500-700 nm.
An often reported technique for incorporating nanostructures into CMOS electronics involves growing nanowires on one substrate, “harvesting” them, and then dispersing them onto the device substrate, which is often referred to as the “pick and place” method. The use of ZnO nanostructures grown directly onto the device substrate is still not widely reported. Fabrication of devices using directly grown nanowires has advantages over more conventional pick and place methods, such as cleanliness and direct placement of nanostructures. In addition to growing well-aligned vertical nanostructures, it would be advantageous if C-axis ZnO films could be fabricated without using costly epitaxial processes.